Residents, many elderly and carrying boxes and bags, fled by boat to the closest neighbouring island of Yakushima, an hour away, where they disembarked shortly before sunset. Several struggled to control excited dogs on leads.

"All I could bring were a few emergency goods. It was utter chaos," one man told Fuji TV. "I'm really worried about things back home."

Smoke shot more than 9,000 metres into the sky and officials warned of more big eruptions and urged "extreme caution".

All Nippon Airways said it would divert some flights as a precaution but it did not cancel any. Japan Airlines said it did not have any plans to change flights.

Island the site of many eruptions in past

Kuchinoerabujima is about 130 kilometres south of Japan's southernmost main island of Kyushu, and 1,000 km southwest of Tokyo.

It was not clear if the eruption would affect the restart of Kyushu Electric Power's Sendai nuclear plant, which on Wednesday cleared the last of the nuclear regulator's safety hurdles, introduced after the Fukushima Daiichi nuclear plant disaster triggered by a March 11, 2011, earthquake and tsunami.

The company said the volcano posed no risk to the Sendai plant on Kyushu, and volcanologists agreed.

The island has seen several eruptions, including one in 1933 that killed eight people, but Mount Shindake was dormant for 34 years until last year.

Japan is one of the world's most seismically active countries and there has been an upsurge in volcanic activity in recent weeks, which volcanologists said may be linked to the big 2011 earthquake that set off a tsunami that killed nearly 20,000 people.

In 2014, 63 people were killed when Mount Ontake in central Japan erupted while packed with hikers.

The volcano erupted suddenly on Friday, blasting plumes of black smoke high into the sky, prompting authorities to order the evacuation of the island's residents and forcing airlines to divert some flights. (Japan Meteorological Agency/Reuters)

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